Vibratory process equipment is used in a wide variety of industrial applications. Vibratory feeders and conveyors, for example, may be used to transport granular material, foundry castings, or other objects. Such feeders and conveyors typically include a bed on which the objects are transported and a drive for producing a vibratory motion of the bed which advances the objects in the desired direction. The drive typically includes an electric motor with eccentric weights mounted on the output shaft. In operation, the output shaft with eccentric weights is rotated to generate vibratory force that is transferred to the bed.
Vibratory process equipment may generally be classified as single mass or two mass systems. In single mass systems, the drive is rigidly connected to the bed and the drive/bed combination is isolated from surrounding terrain by an elastic member. In two mass systems, the drive is elastically coupled to the bed, and either the drive or the bed is isolated from surrounding terrain by an elastic member. Two mass systems are preferable in many applications since they are capable of more efficiently producing vibratory movement. Consequently, a smaller motor may used be used in a two-mass system to produce a force having the same amplitude as that of a single-mass system having a larger motor.
The conventional rotating motors produce a rotational force having an unnecessary and undesired force component. Most vibratory process equipment drives the bed in a desired motion. The rotational force produced by rotating eccentric weights, however, generates a force component that is perpendicular to the desired motion. In two mass systems, the drive is coupled to the bed by an elastic member. The elastic member is typically supported so that it has several degrees of freedom in which to move. A spring, for example, has six primary degrees of freedom (i.e., movement along the X, Y, and Z axes and rotation about the X, Y, and Z axes). As a result, the elastic member may be excited in any number of ways other than in the desired motion. The perpendicular force component may therefore excite the elastic member in undesired directions, thereby detracting from the desired motion and reducing efficiency of the system.
In addition, vibratory process equipment using conventional rotating motors have a rotational inertia that delays stopping and starting of the equipment. As the rotating motors are accelerated from rest to the operating speed, the resulting vibratory force passes through various undesirable frequencies that may excite the connecting or isolation elastic members in undesirable directions. The vibratory force passes through the same undesirable frequencies as the motors decelerate from operating speed to rest. For example, specific frequencies may cause isolation bounce, isolation rock, and rocking between the drive and the bed, among others. These undesirable motions cause extraneous movement of the bed, which may be particularly undesirable for applications requiring quick starting and stopping, such as precision feeders.